1. Field of the Invention
This invention relates to a novel additive composition for automotive fuels, both gasoline and diesel, and to a method for using the composition.
2. The State of the Art
The fuels which are contemplated for use in the fuel compositions of the present invention are normally liquid hydrocarbon fuels in the gasoline boiling range, including hydrocarbon base fuels. The term “petroleum distillate fuel” also is used to describe the fuels which can be utilized in the fuel compositions of the present invention and which have the above characteristic boiling points. The term, however, is not intended to be restricted to straight-run distillate fractions. The distillate fuel can be straight-run distillate fuel, catalytically or thermally cracked (including hydro cracked) distillate fuel, or a mixture of straight-run distillate fuel, naphthas and the like with cracked distillate stocks. Also, the base fuels used in the formation of the fuel compositions of the present invention can be treated in accordance with well-known commercial methods, such as acid or caustic treatment, hydrogenation, solvent refining, clay treatment, etc.
Gasolines are supplied in a number of different grades depending on the type of service for which they are intended. The gasolines utilized in the present invention include those designed as motor and aviation gasolines. Motor gasolines include those defined by ASTM specification D-439-73 and are composed of a mixture of various types of hydrocarbons including aromatics, olefins, paraffins, isoparaffins, napthenes and occasionally diolefins. Motor gasolines normally have a boiling range within the limits of about 70° F. to 450° F. while aviation gasolines have narrower boiling ranges, usually within the limits of about 100° F. to 330° F.
This invention also contemplates the use of diesel fuels. Diesel engines have been employed as engines for over-the-road vehicles because of relatively low fuel costs and improved mileage. However, because of their operating characteristics, diesel engines discharge a larger amount of carbon black particles or very fine condensate particles or agglomerates thereof as compared to the gasoline engine. These particles or condensates are sometimes referred to as “diesel soot”, and the emission of such particles or soot results in pollution and is undesirable. Moreover, diesel soot has been observed to be rich in condensed, polynuclear hydrocarbons, and some of these have been recognized as carcinogenic. Accordingly, particulate traps or filters have been designed for use with diesel engines that are capable of collecting carbon black and condensate particles.
Conventionally, the particulate traps or filters have been composed of a heat-resistant filter element which is formed of porous ceramic or metal fiber and an electric heater for heating and igniting carbon particulates collected by the filter element. The heater is required because the temperatures of the diesel exhaust gas under normal operating conditions are insufficient to burn off the accumulated soot collected in the filter or trap. Generally, temperatures of about 450° C. to 600° C. are required, and the heater provides the necessary increase of the exhaust temperature in order to ignite the particles collected in the trap and to regenerate the trap. Otherwise, there is an accumulation of carbon black, and the trap is eventually plugged causing operational problems due to exhaust back pressure buildup. The above-described heated traps do not provide a complete solution to the problem because the temperature of the exhaust gases is lower than the ignition temperature of carbon particulates while the vehicle runs under normal conditions, and the heat generated by the electric heater is withdrawn by the flowing exhaust gases when the volume of flowing exhaust gases is large. Alternatively, higher temperatures in the trap can be achieved by periodically enriching the air/fuel mixture burned in the diesel engine thereby producing a higher exhaust gas temperature. However, such higher temperatures can cause run-away regeneration leading to high localized temperatures which can damage the trap.
It also has been suggested that the particle build-up in the traps can be controlled by lowering the ignition temperature of the particulates so that the particles begin burning at the lowest possible temperatures. One method of lowering the ignition temperature involves the addition of a combustion improver to the exhaust particulate, and the most practical way to effect the addition of the combustion improver to the exhaust particulate is by adding the combustion improver to the fuel. Copper compounds have been suggested as combustion improvers for fuels including diesel fuels.
The U.S. Environmental Protection Agency (EPA) as of the early 1990s estimated that the average sulfur content of on-highway diesel fuel is approximately 0.25% by weight and had required this level be reduced to no more than 0.05% by weight by Oct. 1, 1993. The EPA also required that this diesel fuel have a minimum cetane index specification of 40 (or meet a maximum aromatics level of 35%). The objective of this rule was to reduce sulfate particulate and carbonaceous and organic particulate emissions. See, Federal Register, Vol. 55, No. 162, Aug. 21, 1990, pp. 34120-34151. Low-sulfur diesel fuels and technology for meeting these emission requirements have not yet been commercially implemented. One approach to meeting these requirements was to provide a low-sulfur diesel fuel additive that could be effectively used in a low-sulfur diesel fuel environment to reduce the ignition temperatures of soot that is collected in the particulate traps of diesel engines.
Various patents, such as U.S. Pat. No. 5,344,467, U.S. Pat. No. 4,340,369, and U.S. Pat. No. 5,376,154, disclosure metal complexes of difunctional organic compounds, including alkali metal salts of difunctional arylsulfonic acids, as fuel additives. Sodium and potassium are the salts of preference. The complex is present in the fuel to provide of up 0.5% by weight of metal (that is, up to 5000 ppm of fuel). The use of alkali earth metal salts of didodecyl benzensulfonic acid for fuel additives is disclosed in U.S. Pat. No. 5,133,900 and U.S. Pat. No. 4,169,564.
U.S. Pat. No. 4,781,730 discloses an alkali metal salt of the reaction product of a polybasic acid and a specified polyhydroxyalkanolamine. Suitable polybasic acids include didodecyl benzenesulfonic acid. Suitable alkali metals are disclosed as including lithium, although the example describes only the use of sodium salts.
U.S. Pat. No. 6,017,369 discloses diesel fuel composition comprising a solution of ethanol, an alkyl ester of a fatty acid, a stabilizing additive selected from the group consisting of (a) a mixture comprising two different ethoxylated fatty alcohols, a cetane booster, and a demulsifier and (b) the reaction product of (1) a mixture of an ethoxylated alcohol and an amide and (2) an ethoxylated fatty acid, and optionally a cosolvent such as naphtha or kerosene. The cetane booster may be t-butyl peroxide. T-butyl peroxide is disclosed in various literature references as a conventional ignition improver or a cetane booster.
U.S. Pat. No. 4,668,247 describes a fuel composition for harnessing the hydrogen energy of a hydrocarbon fuel, comprising 10-90% of a liposoluble organometallic lithium salt and 90-10% of a vehicle oil.